Of the three main couples they teased when that spoiler first appeared, RumBelle is the only one that makes sense because OutlawQueen and CaptainSwan are still in the courting phase. RumBelle is established, and Rumple all but proposed to her when they were reunited in “The New Neverland.” (“The only path I want is the one where you and I are together”) After all they’ve been through, I think it would make complete sense for them to finally say their vows. I’m not sure the show would actually choose to go that route since Rumple and Belle have basically been their star-crossed lovers, but I’d love for them to do so as long as they can keep the relationship and the characters interesting.
If it’s not RumBelle and it’s one of the more minor couples, that would be a bit more anticlimactic. Abigail and David is an interesting thought, although I don’t expect Zelena to actually *succeed* in changing the past. We shall see.